D. Lundell et al., IMPORTANCE OF THE LOOP CONNECTING A-HELIX AND B-HELIX OF HUMAN INTERFERON-GAMMA IN RECOGNITION BY INTERFERON-GAMMA RECEPTOR, The Journal of biological chemistry, 269(23), 1994, pp. 16159-16162
Characterization of murine human hybrid interferon-gamma (IFN-gamma) m
olecules suggests that substitution of the peptide connecting the A an
d B helices in human IFN-gamma with the murine sequence significantly
blocks the protein's binding to the human interferon-gamma receptor. M
utagenesis showed that this effect is localized to the central part of
this A-B loop peptide, particularly Ser(20), Asp(21), Val(22), and Al
a(23). One mutant, IFN-gamma/A23E,D24E,N25K, was examined by NMR. This
''EEK'' mutation does not significantly alter the conformation of int
erferon-gamma, suggesting that the effects of these mutations are not
the result of global conformational changes. The A-B loop is near hist
idine 111, a residue previously shown to be important in receptor-liga
nd interaction (Lunn, C.A., Fossetta, J., Dalgarno, D., Murgolo, N., W
indsor, W., Zavodny, P.J., Narula, S.K., and Lundell, D. (1992) Protei
n Eng. 5, 253-257). We show that copper forms a complex between histid
ine 19 in the A-B loop and histidine 111. This metal complex lacks the
ability to interact with the interferon-gamma receptor. These results
suggest that the A-B loop contains important struc tural information
needed for receptor-ligand binding and hence biological activity of hu
man interferon-gamma.